Receptor tyrosine kinase inhibitors (RTKIs) such as sunitinib, pazopanib and axitinib are effective treatments for clear cell renal cell carcinoma (ccRCC) patients. However, resistance to RTKIs represents a major hurdle in the clinical management of advanced ccRCC. Despite the clinical benefit, acquired resistance to RTKIs occurs within 12 months in the first line setting. Our preliminary data suggest that the expression of the polycomb protein enhancer of zeste homolog2 or EZH2, a histone methyltransferase, may be associated with sunitinib resistance in patient-derived xenograft models (PDXs) and human RCC cell lines. Serendipitously, a reverse- protein phase analysis of our PDX model chronically exposed to sunitinib showed a significant upregulation of the androgen receptor (AR) expression following drug resistance. Interestingly, AR is expressed in RCC and a cross-talk between EZH2 and AR has been proposed in prostate cancer. Our preliminary data also suggest that the combination of sunitinib and either EZH2 or AR inhibitors has greater antitumor effect than single agents both in vitro and in vivo. The overall objective of this application is to determine the role of epigenetics in resistance mechanisms to RTKIs in ccRCC, to assess the epigenomic signature associated with this resistance phenotype, and to develop novel therapeutic strategies to induce epigenetic reprogramming and consequently overcome loss of response to RTKIs. Our central hypothesis is that (acquired and/or innate) resistance to RTKIs may be caused by reversible epigenetic changes and molecular characterization of the resistant phenotype will lead to the identification of novel targets for therapeutic interventions. Taken together, we hypothesize that EZH2 and AR may drive tumor adaption to RTKIs and loss of direct antitumor effect of these drugs in RCC We will test our central hypothesis and, thereby, accomplish the objective of this application by pursuing the following three specific aims: 1) To determine the role of EZH2 and AR in RTKIs resistance in ccRCC models; 2) To assess the impact of EZH2 and AR modulation on reversing RTKIs resistance in ccRCC models; 3) To assess EZH2 and AR status in ccRCC patients and correlate it with response to RTKIs. We expect that these studies will provide 1) a direction to improve RKTI therapy; 2) the epigenetic signature associated with resistance to RTKIs; and 3) preliminary data for novel predictive biomarkers and targets suitable for therapeutic intervention. Taken together, the results from these studies will provide useful information that can be translated in the clinical setting and have an impact in the treatment of advanced kidney cancer.